The present invention relates to screw rotor machines. More specifically, the invention concerns a pair of cooperating rotors for such machines.
In order to increase the volumetric efficiency of a screw compressor, i.e. to increase the delivered amount of air per rotor revolution, it is common to provide the gate rotor with an addendum located outside the pitch circle and the main rotor with a corresponding dedendum located inside the pitch circle. When the gate rotor is provided with such an addendum, a so-called blow-hole is created through which working fluid leaks from a high pressure working chamber to a low pressure working chamber. It is important that this leakage is kept at a minimum in order not to impair the efficiency of the machine.
When screw rotor machines are designed for liquid injection for cooling of the working fluid and for sealing between the rotors and between the rotors and the machine housing, respectively, it is common to exclude the synchronizing gears which otherwise are used to make certain that the rotors rotate without mutual contact. When the rotors are designed to be driven with mutual contact, the rotor profiles must be designed so that gear action is achieved along a portion of the rotor flanks. In previously known rotors of this type, the rotors have been designed so that gear action is achieved inside the pitch circle of the gate rotor flank which is essential for the size of the blow-hole and outside the pitch circle of the main rotor flank which is essential for the size of the blow-hole. Such a design results in a comparatively large blow-hole.